1. Field of the Invention
The present invention relates to an antenna for use in, for example, a wireless communication apparatus such as a mobile communication device or other suitable apparatus. In addition, the present invention relates to a wireless communication apparatus that includes such an antenna.
2. Description of the Related Art
An antenna that is used in a plurality of frequency bands in a wireless communication apparatus such as the terminal device (i.e., mobile phone) of a mobile phone system or the like is described in Japanese Unexamined Patent Application Publication No. 2005-244553 and Japanese Unexamined Patent Application Publication No. 2002-252515. FIG. 1 is a diagram that illustrates the configuration of an antenna that is described in the Japanese Unexamined Patent Application Publication No. 2005-244553. As shown in FIG. 1, an antenna 13 includes a first antenna element 11 and a second antenna element 12 arranged adjacently with respect to a ground plate 8. The first antenna element 11 resonates at a first frequency. The second antenna element 12 resonates at a second frequency. The first antenna element 11 is connected to a first feeding point 14 that is provided on the ground plate 8. One end of a first matching circuit 16 is connected to the first feeding point 14. The other end of the first matching circuit 16 is connected to a connection point 18.
On the other hand, the second antenna element 12 is connected to a second feeding point 15 that is provided on the ground plate 8. One end of a second matching circuit 17 is connected to the second feeding point 15. As in the connection provided for the first antenna element 11, the other end of the second matching circuit 17 is connected to the connection point 18. The connection point 18 is connected to a wireless circuit 7 via a transmission line 6. These components make up a wireless apparatus 19.
The first matching circuit 16 is made up of an inductor 20. The second matching circuit 17 is made up of a capacitor 22 and an inductor 21.
FIG. 2 is a perspective view that illustrates the configuration of an antenna that is described in the Japanese Unexamined Patent Application Publication No. 2002-252515. The illustrated antenna includes two mono antennae 32 and 33 that are arranged in parallel with each other and in the proximity of each other on the surface of an antenna substrate 31. Dielectric substrates 34 and 35 are used as the base substances of the mono antennae 32 and 33, respectively. A strip of radiation electrode 36, 37 is formed on one main surface (e.g., front surface) of each dielectric substrate 34, 35. Except for the periphery of a feeding electrode 39, a ground electrode is formed on the entire region of the other main surface (e.g., rear surface) of each dielectric substrate 34, 35 (it should be noted that the same feeding electrode as the illustrated feeding electrode 39 is formed on the mono antenna 32 though it is not shown therein). A side surface ground electrode 42 is provided on a side surface of each dielectric substrate 34, 35 that extends in the direction of the length thereof (it should be noted that the same side surface ground electrode as the illustrated side surface ground electrode 42 is formed on the mono antenna 33 though it is not shown therein). The two mono antennae 32 and 33 are arranged in such an orientation that these two side surfaces on which these two side surface ground electrodes are arranged face each other. The feeding electrode is connected to the radiation electrode 36, 37 via capacitance therebetween.
However, in the configuration in which two direct feed-type ungrounded mount antennae are used while being fed independently of each other as illustrated in FIG. 1, the problem of interference arises between one of the two direct-feeding non-ground mount antennae and the other. Because of such an interference problem, it is not practically possible to obtain the combined characteristics of one individual direct-feeding non-ground mount antenna and the other individual direct-feeding non-ground mount antenna.
Moreover, if side surface ground electrodes are provided in order to prevent interference from occurring between two mono antennae that are arranged adjacent to each other as illustrated in FIG. 2, the Q value of the antenna increases, which narrows the band characteristics thereof.